Halide reactions and predicting halogen chemistryEdexcel International A Level Chemistry: Subtopic test

1. 1
   A technician tests three unlabelled solid sodium halides, each known to be sodium chloride, sodium bromide or sodium iodide. In a fume cupboard she adds a few drops of concentrated sulfuric acid to a small sample of each and records what happens.

   (a)

   Which observation shows that a sample is sodium chloride?

   [1 mark]

   • AOrange-brown fumes and a colourless, choking gas
   • BSteamy white fumes only, with no coloured vapour
   • CPurple fumes and a yellow solid
   • DA pale yellow gas and a colourless solution

   (b)

   One sample gives hydrogen sulfide among its products. What is the change in the oxidation number of sulfur when H₂SO₄ forms H₂S?

   [1 mark]

   • A+6 to +4
   • B+6 to 0
   • C+6 to +2
   • D+6 to −2

   (c)

   Explain why iodide ions reduce concentrated sulfuric acid but chloride ions do not.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student adds aqueous silver nitrate, acidified with dilute nitric acid, to separate aqueous solutions of potassium chloride, potassium bromide and potassium iodide. She then tests how each precipitate behaves with aqueous ammonia.

   (a)

   What is the colour of the precipitate formed with potassium bromide?

   [1 mark]

   • ACream
   • BWhite
   • CYellow
   • DOrange

   (b)

   Which statement about the precipitates in this experiment is correct?

   [1 mark]

   • ASilver chloride is insoluble in both dilute and concentrated aqueous ammonia
   • BSilver bromide dissolves in dilute aqueous ammonia
   • CSilver iodide does not dissolve in concentrated aqueous ammonia
   • DAll three precipitates dissolve in concentrated aqueous ammonia

   (c)

   Explain why dilute nitric acid is added to the halide solution before the silver nitrate.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Hydrogen chloride gas is made in the laboratory by warming solid sodium chloride with excess concentrated sulfuric acid. In one experiment the gas is passed into a gas jar of ammonia gas. In another it is bubbled into water. Take the molar volume of a gas at room temperature and pressure as 24 dm³ mol⁻¹.

   (a)

   State what is seen when hydrogen chloride gas meets ammonia gas, write the equation for the reaction and state the role of the ammonia.

   [3 marks]

   (b)

   A 5.85 g sample of sodium chloride (relative formula mass 58.5) is warmed with excess concentrated sulfuric acid and the reaction has an 80% yield of hydrogen chloride. Calculate the volume of hydrogen chloride produced, and the maximum mass of ammonium chloride (relative formula mass 53.5) that this gas could form with excess ammonia.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Halogen chemistry changes in a regular way down Group 7. Fluorine and astatine lie at opposite ends of the group. Astatine is radioactive and available only in tiny amounts, so much of its chemistry is predicted from the trends shown by chlorine, bromine and iodine.

   (a)

   Compare the reactions of solid sodium chloride, sodium bromide and sodium iodide with concentrated sulfuric acid, and explain how the results show the trend in reducing ability of the halide ions.

   [6 marks]

   (b)

   Predict the observations when solid sodium fluoride and solid sodium astatide are each warmed with concentrated sulfuric acid, and predict how fluoride and astatide ions behave with aqueous silver nitrate. Explain each prediction using the trends in Group 7.

   [6 marks]

   Total for question 4: 12 marks

End of questions